Building a Multi-region Serverless Application with Amazon API Gateway and AWS Lambda

Many customers are looking to run their services at global scale, deploying their backend to multiple regions. In this post, we describe how to deploy a Serverless API into multiple regions and how to leverage Amazon Route 53 to route the traffic between regions. We use latency-based routing and health checks to achieve an active-active setup that can fail over between regions in case of an issue. We leverage the new regional API endpoint feature in Amazon API Gateway to make this a seamless process for the API client making the requests. This post does not cover the replication of your data, which is another aspect to consider when deploying applications across regions.

Solution overview

Currently, the default API endpoint type in API Gateway is the edge-optimized API endpoint, which enables clients to access an API through an Amazon CloudFront distribution. This typically improves connection time for geographically diverse clients. By default, a custom domain name is globally unique and the edge-optimized API endpoint would invoke a Lambda function in a single region in the case of Lambda integration. You can’t use this type of endpoint with a Route 53 active-active setup and fail-over.

The new regional API endpoint in API Gateway moves the API endpoint into the region and the custom domain name is unique per region. This makes it possible to run a full copy of an API in each region and then use Route 53 to use an active-active setup and failover. The following diagram shows how you do this:

Deploy your Rest API stack, consisting of API Gateway and Lambda, in two regions, such as us-east-1 and us-west-2.

Choose the regional API endpoint type for your API.

Create a custom domain name and choose the regional API endpoint type for that one as well. In both regions, you are configuring the custom domain name to be the same, for example, helloworldapi.replacewithyourcompanyname.com

Use the host name of the custom domain names from each region, for example, xxxxxx.execute-api.us-east-1.amazonaws.com and xxxxxx.execute-api.us-west-2.amazonaws.com, to configure record sets in Route 53 for your client-facing domain name, for example, helloworldapi.replacewithyourcompanyname.com

The above solution provides an active-active setup for your API across the two regions, but you are not doing failover yet. For that to work, set up a health check in Route 53:

A Route 53 health check must have an endpoint to call to check the health of a service. You could do a simple ping of your actual Rest API methods, but instead provide a specific method on your Rest API that does a deep ping. That is, it is a Lambda function that checks the status of all the dependencies.

In the case of the Hello World API, you don’t have any other dependencies. In a real-world scenario, you could check on dependencies as databases, other APIs, and external dependencies. Route 53 health checks themselves cannot use your custom domain name endpoint’s DNS address, so you are going to directly call the API endpoints via their region unique endpoint’s DNS address.

Prerequisites

An S3 bucket in each region in which to deploy the solution, which can be used by the AWS Serverless Application Model (SAM). You can use the following CloudFormation templates to create buckets in us-east-1 and us-west-2:

Deploy both of these using an AWS Serverless Application Model (SAM) template. SAM is a CloudFormation extension that is optimized for serverless, and provides a standard way to create a complete serverless application. You can find the full helloworld-sam.yaml template in the blog-multi-region-serverless-service GitHub repo.

A few things to highlight:

You are using inline Swagger to define your API so you can substitute the current region in the x-amazon-apigateway-integration section.

Most of the Swagger template covers CORS to allow you to test this from a browser.

You are also using substitution to populate the environment variable used by the “Hello World” method with the region into which it is being deployed.

The Swagger allows you to use the same SAM template in both regions.

You can only use SAM from the AWS CLI, so do the following from the command prompt. First, deploy the SAM template in us-east-1 with the following commands, replacing “<your bucket in us-east-1>” with a bucket in your account:

The API was created with the default endpoint type of Edge Optimized. Switch it to Regional. In the Amazon API Gateway console, select the API that you just created and choose the wheel-icon to edit it.

In the edit screen, select the Regional endpoint type and save the API. Do the same in both regions.

Grab the URL for the API in the console by navigating to the method in the prod stage.

Write down the domain name for the URL in each region (for example, 2wkt1cxxxx.execute-api.us-west-2.amazonaws.com), as you need that later when you deploy the Route 53 setup.

Create the custom domain name

Next, create an Amazon API Gateway custom domain name endpoint. As part of using this feature, you must have a hosted zone and domain available to use in Route 53 as well as an SSL certificate that you use with your specific domain name.

You can create the SSL certificate by using AWS Certificate Manager. In the ACM console, choose Get started (if you have no existing certificates) or Request a certificate. Fill out the form with the domain name to use for the custom domain name endpoint, which is the same across the two regions:

You are now ready to create the endpoints. In the Amazon API Gateway console, choose Custom Domain Names, Create Custom Domain Name.

A few things to highlight:

The domain name is the same as what you requested earlier through ACM.

The endpoint configuration should be regional.

Select the ACM Certificate that you created earlier.

You need to create a base path mapping that connects back to your earlier API Gateway endpoint. Set the base path to v1 so you can version your API, and then select the API and the prod stage.

Choose Save. You should see your newly created custom domain name:

Note the value for Target Domain Name as you need that for the next step. Do this for both regions.

Deploy Route 53 setup

Use the global Route 53 service to provide DNS lookup for the Rest API, distributing the traffic in an active-active setup based on latency. You can find the full CloudFormation template in the blog-multi-region-serverless-service GitHub repo.

You can create the stack by using the following link, copying in the domain names from the previous section, your existing hosted zone name, and the main domain name that is created (for example, hellowordapi.replacewithyourcompanyname.com):

The following screenshot shows what the parameters might look like:

Specifically, the domain names that you collected earlier would map according to following:

The domain names from the API Gateway “prod”-stage go into Region1HealthEndpoint and Region2HealthEndpoint.

The domain names from the custom domain name’s target domain name goes into Region1Endpoint and Region2Endpoint.

Using the Rest API from server-side applications

You are now ready to use your setup. First, demonstrate the use of the API from server-side clients. You can demonstrate this by using curl from the command line:

Also, make sure to update the settings in settings.js to match with the API Gateway endpoints for the DNS-proxy and the multi-regional endpoint for the Hello World API: var helloworldMultiregionendpoint = "https://hellowordapi.replacewithyourcompanyname.com/";

You can now open the HTML file in the browser (you can do this directly from the file system) and you should see something like the following screenshot:

You can test failover by changing the environment variable in your health check Lambda function. In the Lambda console, select your health check function and scroll down to the Environment variables section. For the STATUS key, modify the value to fail.

You should see the region switch in the test client:

During an emulated failure like this, the browser might take some additional time to switch over due to connection keep-alive functionality. If you are using a browser like Chrome, you can kill all the connections to see a more immediate fail-over: chrome://net-internals/#sockets

Summary

You have implemented a simple way to do multi-regional serverless applications that fail over seamlessly between regions, either being accessed from the browser or from other applications/services. You achieved this by using the capabilities of Amazon Route 53 to do latency based routing and health checks for fail-over. You unlocked the use of these features in a serverless application by leveraging the new regional endpoint feature of Amazon API Gateway.